This invention relates to a method for manufacturing a buried heterostructure laser diode.
A laser diode which is generally used as a source for optical communications is a buried heterostructure laser diode. The laser diode has mesa interfaces which are (111) In planes between an active region formed during a first epitaxial process and a current blocking layers formed during a second epitaxial growth process. Since the interfaces of the laser diode are exposed to a high temperature of about 600.degree. C, crystal defects may be formed in the interfaces.
Since the damaged interfaces act as a nonradiative recombination center and a current leakage path, major performance indices such as production yield, life-time, stability, lasing threshold current of the diode was deteriorated.
In order to solve the above problems, a conventional approach in which the (111) In planes exposed to high temperatures are melted-back during a second liquid phase epitaxial growth process and then current blocking layers are grown on the clean surface made by the melt-back process was proposed.
By the above approach, buried heterostructure laser diodes having a long life-time and uniform low threshold current was made successfully. But, the above approach required complicated processing conditions and particular subsidary devices in slightly melting-back the damaged (111) In planes and had disadvantages as follows:
In InGaAsP lasers of 1.55.mu.m lasing wavelength range, the InGaAsP surfaces damaged by heat are naturally melted-back during the second growth due to the large compositional difference, and any artificial melt-back process is not necessary. But since InGaAsP active layer with wavelength range of 1.3.mu.m has a small difference in composition from the current blocking layers, and artificial melt-back process was required. Because the melt-back process was carried out using a unsaturated solution with .DELTA.T of 0.2.degree. C for a short time of 15 second close control of solution composition, melt-back time, and temperature were required and other particular devices were also required. It is thus inconvenient and complicated.
Accordingly, it is an object of this invention to provide a simple method for melting-back the damaged (111) In surface of the active layer the second liquid phase epitaxial growth process to solve the above problems.